Hydronic heating ventilating and air conditioning (HVAC) systems for buildings typically include a fluid circuit for delivering heated or chilled water, or other fluids, to occupied spaces in the building. The fluid circuit is typically divided into a number of zones, which can be connected or disconnected from the supply of heated or chilled fluid by zone valves. Such zone valves typically include electric motor driven actuators, which allow the zone valves to be opened or closed from a central location.
Rubber paddle type valves controlled by an electric motor driven actuator, are widely used as zone valves in HVAC systems. Rubber paddle valves typically include a valve body defining an internal passage having a valve seat, and a rubber paddle located within the internal passage that is movable in to, and out of, contact with the seat, for selectively blocking or allowing fluid flow through the internal passage. The rubber paddle is attached to a valve stem which extends through the valve housing for connection to the electric motor driven actuator. The electric motor driven actuator typically includes a return spring, for driving the rubber paddle back to a normally open or a normally closed position when the electric motor of the actuator is not energized.
As shown in FIG. 1, by virtue of their construction, rubber paddle valves typically require forty-five degrees or less of valve stem rotation to move the rubber paddle from a fully open position to a fully closed position, or vice versa. Actuators for use with rubber paddle type valves, are therefore typically designed to limit rotation of the valve stem to an angle of rotation of forty-five degrees or less, with angles of rotation in the range of thirty to forty-seven degrees being typical.
Commonly assigned U.S. Pat. No. 6,073,907 to Schreiner, et al., discloses electric motor driven, rubber paddle valves of the type described above. Schreiner also discloses a releasable engagement structure that provides for a snap-on attachment of the actuator to the body of a valve, and specifically to the body of a rubber paddle type valve.
Although rubber paddle type valves in general, and particularly electric motor driven valves of the type disclosed in Schreiner, work well as zone valves in HVAC systems, there are applications in which it is desirable to utilize a zone valve having higher reliability than can be practically achieved in a rubber paddle type valve.
In particular, it is desirable to use quarter-turn ball valves in zone valve application. Ball valves typically include a rotatable valve element that is formed from metal, or other materials which are more durable than the rubber paddles of the rubber paddle type valve. It is also highly desirable, in such applications, to be able to utilize the same electric motor driven, spring return actuators for driving the ball valves, that were used for driving the rubber paddle type valve.
Unfortunately, as illustrated in FIG. 1, the valve element of a ball valve must be rotated through ninety degrees to move from a fully open to a fully closed position. Spring-return actuators designed for use with rubber paddle valves typically only provide a maximum of forty-five degrees of rotation. If an actuator designed for use with a rubber paddle valve is used for driving a ball valve, the valve member of the ball valve will only be rotated through the first half, approximately, of the full 90 degree range of angular rotation provided by the ball valve.
As will be seen from FIG. 1, the flow through a ball valve is not a linear function of the angular position of the valve member. When the ball valve is initially opening, during the first half of its full 90 degree range of rotation, the slope of the curve depicting flow as a function of angular rotation is considerably flatter that the slope of the curve during the second half of the full 90 degree range of rotation. This results in the ball valve providing significantly less than half of its full flow capacity during the first half of its full 90 degree range of angular rotation, due to the inherent non-linear flow characteristics of the ball valve.
Modifying an existing spring return actuator, designed to provide forty-five degrees or less rotation to a rubber paddle type valve, so that it could provide 90 degrees of rotation and sufficient spring force to drive a ball valve through an angle of rotation of 90 degrees, is typically not possible. In a spring-return actuator, the electric motor must overcome not only the frictional and fluid forces resisting motion of the valve member, but must also work against the return spring. A return spring having enough torque to drive the valve member of a ball valve back to a normally open, or normally closed position, through a 90 degree angle of rotation, would need to be significantly larger than the spring used in an actuator operating over an angle of rotation of forty-five degrees or less. A combination of these factors would require that a spring return actuator capable of driving a ball valve through a full ninety degree angle of rotation would be significantly larger, heavier and more costly than the existing actuators used for driving rubber paddle type valves through an angle of rotation of forty-five degrees or less.
What is needed therefore is an improved apparatus and method for utilizing a ball valve as a zone valve in a HVAC system, preferably in a manner that allows for utilizing existing spring return actuators of the type used for providing forty-five degrees of rotation for rubber paddled type valves for driving the valve member of the ball valve.
In addressing this need, the inventor recognized that if a typical quarter-turn ball valve could be modified to operate over the second half of its angular rotation, i.e. from forty-five degrees to ninety degrees of full opening, existing actuators designed for use with prior rubber paddle type zone valves could be utilized to drive such a modified ball valve.
The inventor also recognized that, although a ball valve used in the second half of its range of angular rotation would typically need to have a higher flow coefficient than a paddle valve of a given size, the ball valve would not necessarily need to have a flow coefficient of twice the paddle valve, due to the steeper slope of the flow vs. angular position characteristic of a ball valve operating in the second half of its angular rotation. Specifically, the inventor recognized that a ball valve operating in the second half of its full 90 degree range of angular rotation would only typically need to be approximately 1.4 times as large as a paddle zone valve being replaced by the ball valve, in order to provide full on-off capability over a range of angular rotation of 45 degrees or less from a fully open position of the valve, because approximately 70 percent of the flow capacity of the ball valve is achieved in the second half of the 90 degree range of angular rotation of the ball valve. Conversely, if a ball valve having a full flow coefficient twice that of the paddle valve being replaced is used, the ball valve would provide significantly more full flow capacity than the paddle valve being replaced over the same angular rotation.
Because a ball valve having twice the full flow capacity of a given paddle type valve is also typically smaller in physical size than the paddle valve being replaced, the inventor further recognized that the need for using a ball valve having a somewhat larger rated capacity than the paddle valve being replaced, in practicing the invention, is not necessarily a disadvantage, and may provide significant advantage where it is desired to have increased full flow capability with the same actuator used with the paddle type zone valve being replaced.